The role of the Hippo-signaling pathway, an evolutionarily conserved organ size control pathway, in cranial bone development and regeneration is poorly understood. We specifically inactivated the Hippo component Salv, and Hippo downstream effectors Yap and Taz in the cranial neural crest (CNC) using the Wnt1cre driver and Wnt1cre2SOR drivers. Salv conditional knock-out (CKO) mutants had dramatically enlarged calvarial bones and cranial sutures with increased calvarial bone density, whereas mutants of Taz homozygous and Yap heterozygous CKO had a range of survival times from E14.5 to postnatal 8 weeks with a range of calvarial bone defects with Wormian bones and decreased calvarial bone density. Notably, our preliminary data suggested that expression and subcellular localization of Yap changes upon Hippo kinase activity, extracellular matrix rigidity and Notch signaling activity. In this proposed K01 study, we investigate the function of Hippo signaling and Yap/Taz mediated signaling crosstalk during cranial bone development and regeneration and will study three aims: 1) To investigate the hypothesis that Hippo signaling and extracellular environment cooperatively regulate osteoblast proliferation and differentiation during cranial bone formation; 2) To investigate the signaling cross talk between Hippo and Notch signaling during cranial bone development; 3) To identify novel target genes of Hippo signaling during cranial bone development and regeneration. My research will focus on bone regeneration and treatment of severely injured bone. This K01 study will provide preliminary data and potential targets in bone regenerative medicine for my subsequent R01 application.